Frac-ball with structurally weakened region

ABSTRACT

A frac-ball for use with a well casing segmentation device and a method of controlling fluid flow through a well casing segmentation device are provided. The frac-ball includes a body having a shell configuration defined by one or more walls, with each wall having an exterior surface and an interior surface. The interior surfaces define an enclosed interior cavity. One or more structurally weakened regions are disposed in the one or more walls.

This application claims priority to U.S. Provisional Patent Application Ser. No. 62/470,558 filed Mar. 13, 2017, which application is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION 1. Technical Field

The present disclosure relates to subterranean well casing segmentation devices in general, and to frac-balls for use in such well casing segmentation devices in particular.

2. Background Information

Subterranean wells can be used to locate and extract subterranean disposed raw materials. For example, wells may be used to locate and extract hydrocarbon materials (e.g., hydrocarbon fluids such as oil, and gases such as natural gas) from subterranean deposits. A water well may be used for locating and extracting potable or non-potable water from an underground water table. A well configured and located to locate and extract hydrocarbon materials typically includes a tubular casing disposed subsurface within the well, and pumping system for injecting materials into and for extracting materials out of the well. The casing may be oriented to have vertically disposed sections, horizontally disposed sections, and sections having a combined vertical and horizontal orientation.

The term “hydraulic fracturing” refers to well formation techniques (sometimes referred to as “well completion” techniques) that create fractures within the subterranean ground to facilitate extraction of hydrocarbon materials disposed within the subterranean ground. There are several hydraulic fracturing techniques currently used, including techniques that utilize fluid flow segmentation devices.

For example, “plug and perforation” techniques may utilize one or more plugs (a type of casing segmentation device) that are positionable within the well casing. The plugs are used to fluidically isolate casing sections (i.e., segment the casing into “zones”) for a variety of reasons; e.g., to permit specific casing sections to be radially perforated, etc. The perforations in the casing provide fluid paths for materials to selectively exit and enter a fluid passage within the casing. In some instances, the plugs are designed to include a fluid flow passage that permits fluid flow through the plug; i.e., between a forward end of the plug and an aft end of the plug. The passage has a ball seat disposed at or near the forward end of the passage. The term “forward end” refers to the end of the plug fluid flow passage disposed closest to the well head when disposed within the casing, and the term “aft end” refers to the end of the plug fluid flow passage disposed farthest from the well head when disposed within the casing. The passage ball seat is configured to receive a ball (sometimes referred to as a “frac-ball”). To segment the well casing, a frac-ball is introduced into the casing and the frac-ball is carried with fluid flow until it reaches the ball seat. Once the frac-ball is seated properly within the seat, the frac-ball closes the plug fluid passage and prevents fluid passage through the plug. The fluid on one side of the plug may then be increased dramatically in pressure; e.g., to perform the perforation/fracturing process.

Once all of the zones are fractured, it is necessary to remove the frac-balls to permit fluid travel within the casing. It is known in the prior art to machine out a frac-ball and ball seat, but such a process is time-consuming and expensive. It is also known in the prior art to use a frac-ball made of a material that dissolves or erodes over time within the well fluid environment. These methods are not desirable because the dissolving or eroding process takes a considerable amount of time. In fact, the rate of dissolution or erosion can vary significantly depending on environmental conditions within the well, and consequently it may be unclear whether a frac-ball is removed or not at a given point in time. These type frac-balls also do not remove the ball seat. As a result, the balls seat can act as a flow impediment.

What is needed is a frac-ball that overcomes the issues associated with existing technology.

SUMMARY OF THE DISCLOSURE

According to an aspect of the present disclosure, a frac-ball for use with a well casing segmentation device is provided. The frac-ball includes a body having a shell configuration defined by one or more walls, with each wall having an exterior surface and an interior surface. The interior surfaces define an enclosed interior cavity. One or more structurally weakened regions are disposed in the one or more walls.

According to another aspect of the present disclosure, a method of controlling fluid flow through a well casing segmentation device is provided. The method includes: a) disposing an impermeable frac-ball in a seat of a well casing segmentation device to close a fluid passage of the well casing segmentation device, wherein the frac-ball includes at least one structurally weakened region; and b) causing an elevated pressure event adequate to cause the at least one structurally weakened region to fail, thereby opening the fluid passage of the well casing segmentation device.

In any of the aspects or embodiments described above and herein, the one or more structurally weakened regions have at least one physical characteristic different from a portion of the wall surrounding the structurally weakened region.

In any of the aspects or embodiments described above and herein, the one or more structurally weakened regions may each possess mechanical strength properties adequate to avoid failure within a range of predetermined well environment operating parameters and/or for a predetermined period of time in a well casing environment.

In any of the aspects or embodiments described above and herein, the one or more walls may each have a thickness extending between the exterior surface and the interior surface, and at least one of the structurally weakened regions is a pocket disposed in the wall, which pocket results in a decreased wall thickness.

In any of the aspects or embodiments described above and herein, a pocket may be disposed in the interior surface of the wall, or in the exterior surface of the wall, or in both.

In any of the aspects or embodiments described above and herein, the frac-ball may include an energetic material and a trigger mechanism, the trigger mechanism configured to selectively initiate the energetic material.

In any of the aspects or embodiments described above and herein, the energetic material and trigger mechanism may be disposed within the interior cavity of the frac-ball.

In any of the aspects or embodiments described above and herein, the energetic material and trigger mechanism may be configured to produce an elevated pressure event adequate to cause the structurally weakened regions to fail.

In any of the aspects or embodiments described above and herein, the energetic material and trigger mechanism may be configured to produce an elevated pressure event within the interior cavity adequate to cause the structurally weakened regions to fail in a manner that causes the frac-ball to rupture into discrete pieces.

In any of the aspects or embodiments described above and herein, the energetic material and trigger mechanism may be configured to produce an elevated pressure event within the interior cavity adequate to cause the structurally weakened regions to fail in a manner that produces fluid passages through the frac-ball.

In any of the aspects or embodiments described above and herein, the one or more structurally weakened regions disposed in the one or more walls may each include a plug disposed within an aperture disposed within the one or more walls, and the energetic material and trigger mechanism may be configured to produce an elevated pressure event within the interior cavity adequate to cause each plug to dislodge from the one or more walls.

In any of the aspects or embodiments described above and herein, the frac-ball body may be comprised of a first material that erodes, corrodes, or dissolves at a first rate when contacted with a well casing fluid, and a plug comprised of a second material that erodes, corrodes, or dissolves at a second rate when contacted with a well casing fluid is disposed in each structurally weakened region, and the second rate is greater than the first rate.

In any of the aspects or embodiments described above and herein, the frac-ball may include an interior cavity and an energetic material and a trigger mechanism disposed within the interior cavity, the trigger mechanism may be configured to selectively initiate the energetic material, and the step of causing the elevated pressure event adequate to cause the at least one structurally weakened region to fail includes the trigger mechanism initiating the energetic material.

In any of the aspects or embodiments described above and herein, the at least one structurally weakened region may be configured to fail in a manner that causes the frac-ball to rupture into discrete pieces upon initiation of the energetic material.

In any of the aspects or embodiments described above and herein, the at least one structurally weakened region may be configured to fail in a manner that produces one or more fluid passages through the frac-ball upon initiation of the energetic material.

The foregoing features and the operation of the present disclosure will become more apparent in light of the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional diagrammatic illustration of a portion of a well casing.

FIG. 2 is a diagrammatic illustration of a casing segmentation device.

FIG. 3 is a diagrammatic view of a frac-ball embodiment.

FIG. 4 is a diagrammatic sectioned view of a frac-ball embodiment.

FIG. 5 is a diagrammatic view of a frac-ball embodiment.

FIG. 6 is a diagrammatic sectioned view of a frac-ball embodiment.

FIG. 7 is a diagrammatic view of a frac-ball body having a first body portion and a second body portion displaced side-by side.

FIG. 8 is a diagrammatic sectioned partial view of a frac-ball embodiment.

FIG. 8A is a diagrammatic sectioned partial view of a frac-ball embodiment.

FIG. 9 is a diagrammatic sectioned partial view of a frac-ball embodiment.

FIG. 10 is a diagrammatic sectioned view of a frac-ball embodiment.

FIG. 11 is a schematic diagram illustrating a trigger mechanism and energetic material.

FIG. 12 is a diagrammatic sectioned view of a frac-ball embodiment.

The present method and advantages associated therewith will become more readily apparent in view of the detailed description provided below, including the accompanying drawings.

DETAILED DESCRIPTION

Now referring to FIG. 1, an exemplary embodiment of a wellbore 20 disposed in a subterranean formation is shown. The wellbore 20 includes a fluid conduit (typically referred to as a “casing”; e.g., casing 22) disposed within a drilled bore extending below surface level 24. The wellbore 20 is diagrammatically shown as having a substantially vertical oriented section 26, a substantially horizontal oriented section 28, and an arcuate section 30 connecting the vertical and horizontal sections 26, 28. For purposes of describing aspects of the present disclosure, the casing 22 is described herein as including well casing segmentation devices 32, packers 34, and pipe sections 36. The pipe sections 36 include a wall 38 surrounding a flow passage 40. The described well casing configuration reflects a typical configuration and the present disclosure is not limited to any particular well casing configuration. The casing 22 is disposed within the well after the well is drilled. The wellbore 20 is shown as having cement 42 disposed between the outer diameter of the casing 22 and the inner diameter of the drilled bore, which cement 42 secures the casing 22 within the drilled bore. Not all wellbores include cement or other material disposed outside of the casing 22.

As indicated above, a well completion process that utilizes hydraulic fracturing involves creating fractures 44 (e.g., cavities) within the subterranean ground adjacent the casing 22 to facilitate extraction of hydrocarbon materials (or water) disposed within the subterranean ground. The fracturing process is typically performed in segments (sometimes referred to as “stages” or “zones”); e.g., a first segment of the casing 22 may be created adjacent the portion of the wellbore 20 furthest from the wellhead 46 (e.g., using a well casing segmentation device 32), and the casing 22 in that segment “perforated” to create a fluid path between the casing flow passage 40 and the subterranean environment adjacent the segment. Once the first segment is fractured, that segment may be isolated, and the process may be repeated for the next segment in line, until the all of the desired segments of the wellbore 20 are fractured. The term “perforated”, as used herein, refers to the creation of the aforesaid fluid paths between the casing flow passage 40 and the subterranean environment adjacent the segment. A pipe section 36 of the casing 22 may be perforated by creating holes in the wall 38 of the pipe section 36 (e.g., using a perforating gun or a sliding sleeve type device). The present disclosure is not limited to use with any particular device or method for creating the fractures within the subterranean environment. As is known in the prior art, segmentation devices 32 may utilize frac-balls for the purpose of establishing a sealed segmentation device that is operable to isolate certain segments of the well casing 22.

As indicated above, well casing segmentation devices 32 (sometimes referred to as “plugs”) can be used to selectively create fluid flow barriers within a well casing 22. FIG. 2 diagrammatically illustrates a well casing segmentation device 32 having a fluid flow passage 33 and a seat 35 for receiving a seal element 50 (referred to hereinafter as a “frac-ball”). The seat 35 and frac-ball 50 may be described as having mating geometries. Once the frac-ball 50 is properly engaged within the seat 35, the frac-ball 50 closes the fluid passage 33 and prevents fluid passage there through. A difference in pressure across the frac-ball 50 may be used to maintain the engagement of the frac-ball 50 with the seat 35.

Now referring to FIGS. 3-9, in some embodiments a frac-ball 50 according to the present disclosure includes a body 52 having a shell configuration defined by one or more walls 54, with each wall 54 having an exterior surface 56 and an interior surface 58. The interior surfaces 56 define an enclosed interior cavity 60. The thickness of the wall 54 is defined as the shortest distance between an interior surface 58 and the exterior surface 56 (e.g., extending along a line extending radially outwardly from the center of a spherical shell passing through the interior and exterior surfaces 56, 58, or a line passing through the surfaces 56, 58 that is substantially normal to both surfaces, etc.). FIGS. 3 and 5 are planar diagrammatic views of a frac-ball body 52 embodiments in a hollow sphere configuration, and FIGS. 4 and 6 are sectioned views of frac-ball 50 embodiments. The walls 54 of the hollow sphere configuration define an enclosed interior cavity 60. The present disclosure is not limited to frac-balls 50 having a hollow sphere configuration.

A frac-ball 50 according to the present disclosure may be formed as a unitary body or may be formed as a plurality of independent pieces that are combined to produce the frac-ball 50. FIGS. 4 and 7, for example, illustrate a frac-ball 50 embodiment that includes a first body portion 62 and a second body portion 64 that combine together to form the frac-ball body 52. The two body portions 62, 64 may include male and female features that mate with one another to facilitate the connection between the two body portions. For example, the first body portion 62 shown in FIGS. 4 and 7 includes an inside flange 66 having screw threads disposed on an exterior surface of the inside flange 66, and the second body portion 64 includes screw threads disposed on an interior surface. The first and second body portions 62, 64 are combined together by engaging the respective threaded portions together. The body portions 62, 64 may be held together thereafter, solely by the threaded portions, or the threaded portions in combination with another attachment mechanism (e.g., adhesive, weld, braze, etc.) The above described mechanism for joining body portions of a frac-ball 50 into a single body is a non-limiting example of an attachment mechanism. In addition, the present disclosure is not limited to a having a unitary body or a two-piece constructions; e.g., the body 52 may be formed from more than two body portions. The frac-ball body 52 (with the exception of the structurally weakened regions as will be described below) possesses adequate mechanical strength properties to function as a sealing element within a well segmentation device within a range of predetermined well environment operating parameters and/or for a predetermined period of time in a well casing environment, which operating parameters are those parameters known to be present or typical within the aforesaid well casing environment. In this state where it functions as a sealing element within a well segmentation device, the frac-ball 50 may be described as being impermeable; i.e., it does not permit fluid flow through the well casing segmentation device.

The walls 54 of the frac-ball 50 include one or more structurally weakened regions 68. The term “structurally weakened region” as used herein describes a region of the frac-ball wall 54 having at least one physical characteristic different from the wall portion surrounding the structurally weakened region 68, which characteristic is such that the structurally weakened region 68 will fail before the wall portion surrounding the structurally weakened region 68 fails, or will precipitate a failure of the surrounding wall when both are subjected to the same conditions. The structurally weakened region 68 possesses adequate mechanical strength properties to avoid failure or breach within a range of predetermined well environment operating parameters (e.g., well casing environmental conditions typically present when the frac-ball 50 operates to seal a well casing segmentation device) and/or for a predetermined period of time in a well casing environment, but can be caused to fail or breach when subject to certain conditions. For example, a structurally weakened region 68 may be designed to seal and hold mechanical integrity to a maximum fracing differential pressure. The differential pressure is the difference in pressure at the well casing segmentation device 32 with mated frac ball 50, between the pressurized “top” side and the local condition “bottom” side of the device/mated frac-ball. The anticipated maximum differential pressure is typically about 8000 psi. In many instances, a structurally weakened region may be designed to be about 1.15 to 1.20 times stronger than the maximum anticipated differential pressure across the frac-ball 50, whereas the frac-ball wall regions away from the structurally weakened regions are typically at least 1.40 to 1.50 times stronger than the maximum anticipated differential pressure across the frac-ball 50. The present disclosure is not limited to these ranges.

A structurally weakened region may be provided in a variety of different configurations. For example, in some embodiments the structurally weakened region 68 may comprise a physical characteristic (e.g., a physical feature that creates a stress concentration factor, or a weakened area, etc.) that will precipitate a failure or breach of the wall portion surrounding the structurally weakened region 68 under certain conditions. The failure or breach of a single structurally weakened region 68 may be adequate to transform the frac-ball from a structure that is able to close the well casing segmentation device to fluid flow, to one that cannot prevent fluid flow there through, thereby opening the well casing segmentation device to fluid flow. In some embodiments, the frac-ball may include a plurality of structurally weakened regions 68, each comprising a physical characteristic that will precipitate a failure or breach of the wall portion surrounding the structurally weakened region 68 under certain conditions. In any of these embodiments, the failure or breach of the structurally weakened region(s) may be adequate to cause the frac-ball to fracture into a plurality of discrete pieces, each smaller in size that the original frac-ball 50. In these embodiments, the fracturing of the frac-ball into a plurality of discrete pieces is facilitated as compared to fracturing a frac-ball into pieces that does not include the structurally weakened region(s). The term “discrete pieces” as used herein describes pieces that are created as a result of the frac-ball rupturing as opposed to granular sized material eroded or dissolved from the frac-ball.

In some embodiments, the structurally weakened regions may be configured such that the structurally weakened region will fail or breach, but the frac-ball body will remain intact. The breached structurally weakened regions permit fluid flow through the frac-ball; e.g., fluid flow passages extending through the breached structurally weakened regions and the interior cavity. Consequently, the well casing segmentation device changes from a closed state to an open state.

A non-limiting example of a structurally weakened region 68 is a region of a frac-ball wall 54 having a decreased thickness relative to the wall portion surrounding the structurally weakened region 68. As a specific non-limiting example of such a structurally weakened region 68, a pocket 70 (e.g., see FIGS. 4-8) may be disposed in the frac-ball wall 54, with the pocket 70 having an open end 72 disposed at the interior surface 58 of the frac-ball 50, which open end 72 is open to the interior cavity 60 of the frac-ball 50, a base end 74, and one or more side walls 76 extending between the open end 72 and the base end 74 (i.e., an “interior wall pocket”). The pocket 70 includes a depth dimension (“PD”) extending between the open end 72 and the base end 74, and at least one width (“PW”) extending between opposing side walls 76 or side wall portions (e.g., a cylindrical configuration pocket may be described as having a single width, whereas a rectangular pocket may have two different widths, etc.). The pockets 70 shown in FIGS. 3-6 have a cylindrical configuration. Structurally weakened regions 68 in the form of a pocket 70 may assume a variety of different geometric configurations (e.g., cylindrical, parti-spherical, elliptical, polygonal, rectangular, circumferentially extending slots, etc.) and are not limited to any particular geometric configuration. In addition, a frac-ball 50 according to the present disclosure may include a plurality of pockets 70 with one or more having a geometric configuration that differs from the geometric configuration of another. The frac-ball may include a plurality of different structurally weakened regions 68 disposed in coordination with one another; e.g., configured and combined such that failure of one precipitates failures of others, thereby leading to fracturing of the frac-ball into discrete pieces. The depth of the pocket (i.e., “PD”) disposed within the frac-ball wall 54, decreases the wall 54 thickness (e.g., “X”) to a dimension (“X′”) equal to the difference between “X” and “PD” (i.e., X-PD=X′). In this example of a structurally weakened region 68, the at least one physical characteristic different from the wall portion surrounding the structurally weakened region 68 is the decreased wall 54 thickness; e.g., the decreased wall thickness factors in the structurally weakened region 68 failing before the wall portion surrounding the structurally weakened region 68.

Now referring to FIGS. 5 and 6, in some frac-ball 50 embodiments one or more pockets 70 may be disposed extending into the wall 54 from the exterior wall surface 56 of the frac-ball 50 (i.e., an “exterior wall pocket”).

Now referring to FIG. 8, in some embodiments the frac-ball 50 may include one or more pockets 70 extending into the wall 54 from the interior surface 58 of the frac-ball interior cavity 60 and one or more pockets 70 disposed extending into the wall 54 from the exterior wall surface 56 of the frac-ball 50 (e.g., a combination of interior and exterior wall pockets). In addition, an interior wall pocket 70 may be aligned with an exterior wall pocket 70. The present disclosure is not limited to any particular configuration of wall pockets 70.

Now referring to FIG. 9, another example of a physical characteristic that can define a structurally weakened region 68 within the frac-ball wall 54 is a region of the frac-ball 50 comprised of a dissimilar material. For example, a frac-ball 50 may have walls 54 formed of a first material that erodes, corrodes, or dissolves at a first rate when subjected to well casing fluids. Such a frac-ball 50 may have structurally weakened regions 68 in the form of a plurality of apertures 68A (or pockets) disposed within the wall(s) 54 filled with a second material plug 78. The apertures 68A extend between the exterior wall surface 56 and the interior wall surface 58. The second material plugs 78 are comprised of a material dissimilar to the frac-ball first material. The second material erodes, corrodes, or dissolves at a second rate when subjected to well casing fluids, which second rate is faster than the first rate. After the frac-ball 50 is subjected to well casing fluids for a sufficient period of time, the second material erodes, corrodes, or dissolves. Once a sufficient amount of the second material has eroded, corroded, or dissolved, fluid flow may pass through the frac-ball via the wall apertures 68A, or the remaining pockets may be structurally inadequate and the wall may be breached and/or the frac-ball ruptured into discrete pieces. As a result, fluid may flow through the frac-ball 50 (or through the well casing segmentation seat in the event of frac-ball rupture. The second material may be disposed only within the frac-ball wall apertures 68A, or may be disposed in the apertures 68A as well as the interior cavity 60 of the frac-ball 50.

FIG. 10 illustrates another example of a structurally weakened region 68 that includes a dissimilar material. Here again, the frac-ball 50 has walls 54 formed of a first material that erodes, corrodes, or dissolves at a first rate when subjected to well casing fluids, and includes a plurality of apertures 68B. In this embodiment, however, the frac-ball 50 does not have a shell configuration. Rather, the frac-ball body 52 is a solid body comprised of the first material except for apertures 68B that extend entirely through the frac-ball body 52; e.g., apertures that extend between opposite exterior wall surfaces 56. The apertures 68B are filled with a plug 78 comprised of a second material. The second material is dissimilar to the frac-ball 50 first material. The second material erodes, corrodes, or dissolves at a second rate when subjected to well casing fluids, which second rate is faster than the first rate. After the frac-ball 50 is subjected to well casing fluids for a sufficient period of time, the second material erodes, corrodes, or dissolves and the second material no longer prevents fluid flow through the frac-ball wall apertures 68B. As a result, fluid may flow through the frac-ball 50. The diagrammatic example shown in FIG. 10 depicts apertures 68B that are orthogonally oriented and intersecting with one another. The present disclosure is not limited to particular aperture 68B configuration, including this example.

Now referring to FIG. 8A, in some embodiments a frac-ball 50 may have walls 54 that include apertures 68C disposed within the walls 54 that extend between the exterior wall surface 56 and the interior wall surface 58, and plugs 82 disposed within the apertures 68C. The plugs 82 have an asymmetric configuration that prevents them from passing radially inward. For example, FIG. 8A shows a first plug 82A having a first asymmetric configuration (e.g., a truncated cone with an exterior diameter larger than an interior diameter) and a second plug 82B having a second asymmetric configuration (e.g., a T-shaped configuration with a cap portion having a first diameter, and a stem portion having a second diameter, small than the first diameter). These asymmetric plug configurations 82A, 82B are non-limiting examples. In these embodiments, the frac-ball 50 and the plug 82 may comprise the same material or may comprise different materials. The frac-ball 50 and the plug 82 may both comprise a material(s) that erodes, corrodes, or dissolves when subjected to well casing fluids. The plugs 82 may be attached to the frac-ball 50 by any acceptable means; e.g., an adhesive, welding, brazing, mechanical fit (e.g., a press fit), etc. As will be described below, an energetic material (e.g., an explosive material) disposed within the interior cavity 60 of the frac-ball 50 may be used to dislodge the plug 82 from the frac-ball body 52 and thereby provide one or more fluid passages through the frac-ball 50, or cause the frac-ball wall 54 to fail and fracture into discrete pieces. In these embodiments, the apertures 68C and the plugs 82 provide structurally weakened regions 68 within the frac-ball wall 54; e.g., structurally weakened regions in a radially outward direction.

As described above, some frac-ball 50 embodiments according to the present disclosure may be configured to remain intact, but permit fluid flow there through, upon failure of a plurality of weakened structural regions 68. For example, failed weakened structural regions 68 may permit fluid passage through the frac-ball 50; e.g., well casing fluids may enter a first frac-ball wall portion via one or more failed structurally weakened regions 68, and subsequently exit the frac-ball wall 54 via one or more failed structurally weakened regions 68 in a second wall portion.

In some embodiments, a frac-ball 50 may include a predetermined failure mechanism configured to cause the structurally weakened regions 68 to fail or be breached. In one example, the predetermined failure mechanism may include an energetic material 80 (e.g., an explosive material) disposed within the interior cavity of the frac-ball 50 (e.g., see FIG. 6). The detonation of the energetic material 80 is sufficient to cause the structurally weakened regions 68 to fail or be breached. For example, the detonation of the energetic material 80 is adequate to rupture or fracture (e.g., mechanically fail) the structurally weakened regions 68. As a result, the failed structurally weakened regions either precipitate failure of the remainder of the frac-ball into discrete pieces, or create one or more fluid passages through the otherwise intact frac-ball 50. More specifically, the detonation of the energetic material 80 creates an elevated pressure event (i.e., a substantial rise in the pressure within the interior cavity 60 of the frac-ball 50) of a magnitude that is adequate to fail/breach preferably all of the structurally weakened regions 68. Typically, the elevated pressure event produces an amount of force that is beyond the material strength of the structurally weakened region and the amount of external fluid force acting on the structurally weakened region. In most fracing operations, it is believed that an elevated pressure event that produces a pressure within the interior cavity that is five to seven times (5-7 times) greater than the maximum external fracing pressure will be adequate. The specific amount of pressure required to cause the structurally weakened regions to fail or breach may vary depending on the characteristics of the frac-ball and the application. Once the structurally weakened regions 68 are ruptured, the remaining portions of the frac-ball rupture into discrete pieces, or fluid passages through the frac-ball 50 are created. Once the structurally weakened regions 68 rupture (and possibly other wall portions fail), the frac-ball 50 is no longer capable of preventing fluid flow through the segmentation device.

In those embodiments wherein the predetermined failure mechanism includes an energetic material 80 disposed within the frac-ball 50, the interior cavity 60 of the frac-ball 50 may contain a liquid (or gel) considered to be substantially incompressible. Upon detonation of the energetic material 80, energy created by the energetic material 80 (e.g., the elevated pressure event) is transmitted into the liquid, which would subsequently be transmitted to the frac-ball body 52 (e.g., via shock wave), thereby causing the frac-ball body 52 to fracture into the aforesaid discrete pieces or have passages breached. FIG. 12 includes a fill port 99 that could be used to fill the frac-ball interior cavity 60 with such a liquid. Upon the frac-ball being fractured or breached, the liquid would subsequently mix with the fluid disposed within the well casing. Non-limiting examples of fluid core materials include water, mineral oil, ballistic gelatin, and silicon oil. Fluid materials (e.g., oils, ballistic gelatin, etc.) that have no adverse effect on trigger mechanism electronics are particularly useful.

Non-limiting examples of an energetic material 80 (e.g., an explosive material) that may be used with frac-balls 50 of the present disclosure include lead azide, zirconium potassium perchlorate (ZPP), gasless ignition powders such as AlA (e.g., comprising Zirconium powder, Ferric oxide, and diatomaceous earth), pentaerythritol tetranitrate (PETN), cyclotrimethylenetrinitramine (RDX), and diazodinitrophenol (DDNP).

For those embodiments that include an energetic material failure mechanism, the mechanism may be disposed within the frac-ball 50 in a form that can be initiated by a selectively operable trigger mechanism 84.

A trigger mechanism 84 may assume a variety of different forms, and the present disclosure is not limited to any particular type of trigger mechanism 84. The trigger mechanism 84 may include electronic circuitry (digital or analog) capable of executing logical functions (referred to hereinafter generically as a “logic controller 86”; see FIG. 11). For example, the trigger mechanism 84 may include a logic controller 86 that includes electronic hardware components capable of executing logic functions. As another example of such a logic controller 86, a trigger mechanism 84 may include one or more processors capable of processing stored instructions (e.g., instructions stored in a memory device included directly with the processor, or one separate from, but in communication with, the processor). A trigger mechanism 84 may also include one or more sensors 90 (e.g., temperature sensors, pressure sensors, magnetic, electromagnetic, conductivity, etc.), timing devices 92, receivers 94 (e.g., adapted to RF signals, ultrasonic signals, pressure pulse signals, etc.) and/or receiver-transmitters, an energy source 96 (e.g., a battery), one or more detonators 98, etc., including any combination thereof. The aforesaid sensors 90, timing devices 92, receivers 94, energy source 96, detonators 98, etc., may be in communication with the logic controller 86 via electronic circuitry.

A first example of a type of trigger mechanism 84 is one that is temperature activated. Some wells have well portions where the subterranean environment is at elevated temperature. In these applications, a fracturing fluid that is being pumped from the surface may be no warmer than a known temperature (e.g., 80° F.) and during fracturing the aforesaid fluid will maintain a frac-ball 50 at a temperature that is cooler than the surrounding well environment; e.g., the fracking fluid acts as a coolant. Once the fracturing operation at a stage is complete, the warmer temperature reservoir fluids and gases will raise the temperature of the frac-ball 50 via thermal conduction and/or convection. In this instance, the trigger mechanism 84 may be disabled below a predetermined temperature, and enabled at temperatures above the predetermined temperature. A temperature sensor 90 portion of the trigger mechanism 84 provides a signal indicative of the temperature to a logic controller 86 portion of the trigger mechanism 84. Once a predetermined temperature (e.g., “a trigger temperature”) is sensed, the logic controller 86 executes logic that directly or indirectly initiates the energetic material. Alternatively or in combination with a temperature sensor 90, the trigger mechanism 84 may include a temperature activated bimetallic device (not shown). A bimetallic device may include a first metallic alloy and a second metallic alloy. The first metallic alloy has a first melting temperature and the second metallic alloy has a second melting temperature, which second melting temperature is higher than the first melting temperature. The first metallic alloy and the second metallic alloy are exothermically reactive with one another, and are initially separated from one another. The first metallic alloy is selected to have a melting temperature that coincides with the desired trigger temperature. When the first metallic alloy reaches the trigger temperature it melts, begins to flow, and contacts the second metallic alloy, thereby triggering an exothermic reaction between the two alloys. The exothermic reaction between the alloys may be the mechanism that causes detonation of the energetic material 80.

Another type of trigger mechanism 84 is one that is pressure activated. For example, the trigger mechanism 84 may include a pressure sensor 90 that is in communication with a logic controller 86. When the pressure sensor 90 communicates to the logic controller 86 that a predetermined environmental pressure is present, the logic controller directly or indirectly initiates the energetic material 80. The predetermined pressure could be the high pressure resultant from a fracturing operation or it could simply be the hydrostatic pressure exerted by the column of fluid in the well. For example, FIG. 12 diagrammatically illustrates a frac-ball 50 embodiment that includes a trigger mechanism 84 (having logic controller 86) and energetic material 80 disposed in the interior cavity 60 of the frac-ball 50. A pair of pressure sensors 90 are shown mounted in the walls of the frac-ball body 52. The pressure sensors 90 sense the pressure in the well casing fluid and communicate signals to the logic controller 86 portion of the trigger mechanism 84 indicative of the environmental pressure. When the aforesaid sensors indicate the environmental pressure is at or above a predetermined value (e.g., a predetermined threshold), the logic controller 86 directly or indirectly initiate the energetic material 80. The predetermined pressure could be the high pressure resultant from a fracturing operation or it could simply be the hydrostatic pressure exerted by the column of fluid in the well.

Another type of trigger mechanism 84 is one that activates upon receipt or termination of a selectively emitted signal. For example, the trigger mechanism 84 may include a signal receiver 94 (which may be in the form of a pressure sensor 90), in communication with a logic controller 86. Signals received by the receiver 94 (e.g., radio frequency energy type signal, acoustic energy type signals, pressure pulse type signals, etc.) are communicated to a logic controller 86. The logic controller 86 causes the selective detonation of the energetic material 80.

Another type of trigger mechanism 84 is one that actuates based on timing; e.g., the trigger mechanism 84 can include a timer mechanism 92 in communication with a logic controller 86 that initiates detonation at a particular time, or after a predetermined interval of time.

Another type of trigger mechanism 84 is one where the frac-ball 50 is physically processed prior to deployment. For example, the trigger mechanism 84 can be configured to activate upon the frac-ball 50 being spun at a predetermined rotational speed (e.g., “X” rotations per minute—“RPMs”) to arm the device prior to deployment.

In some embodiments, a trigger mechanism 84 may include one or more safety features. For example, the trigger mechanism 84 may be configured to include an activating sequence that includes an inhibit whereby prior to detonation of an energetic material, the trigger mechanism will query its surroundings to verify certain predetermined conditions. If the condition is satisfied, then the trigger mechanism 84 will initiate rupture or breach of the frac-ball 50.

In some embodiments, where a frac-ball includes a predetermined failure mechanism that includes an energetic material 80 (e.g., an explosive material) disposed within the interior cavity of the frac-ball 50 (e.g., see FIG. 5), and the frac-ball includes plugs 82 disposed within its walls 54, the detonation of the energetic material 80 creates an elevated pressure event of a magnitude that is adequate to dislodge the plugs 82. Dislodging the plugs 82 from the frac-ball 50 body will create one or more fluid passages through the frac-ball 50, or cause the frac-ball wall to fail and fracture into discrete pieces.

In an alternative embodiment, the predetermined fracture mechanism may involve erosion, corrosion, or dissolution of structurally weakened regions 68 disposed within a frac-ball 50. The eroding or dissolving material disposed in the structurally weakened regions 68 may be the same material as the remainder of the frac-ball body 52, but due to the decreased wall thickness of the structurally weakened region 68, it fails (e.g., creates a breach) before the frac-ball body 52 as a whole substantially erodes, corrodes, or dissolves. Once the structurally weakened regions 68 have failed, fluid is able to flow through frac-ball 50. Also as indicated above, the material disposed in the structurally weakened regions 68 may alternatively comprise a material dissimilar to the frac-ball body portion surrounding the respective structurally weakened regions 68; i.e., one that erodes, corrodes, or dissolves faster than the material of the frac-ball portion surrounding the structurally weakened region 68.

A significant aspect of the present disclosure relates to the ability of well casing fluid to not only enter and pass through the frac-ball 50, but also the increased amount of frac-ball 50 surface area exposed to well casing fluid. As indicated above, a frac-ball 50 may be comprised of one or more materials that will either erode, corrode, or dissolve when exposed to well casing fluids. Prior art frac-balls of which we are aware do not include internal passages that permit well casing fluid to pass through the frac-ball. As a result, only the external surface area of the frac-ball is exposed to well casing fluid. Hence, any erosion, corrosion, or dissolution of these type frac-balls necessarily takes place at the external surface. Frac-balls 50 according to the present disclosure, on the other hand, allow well-casing fluids to enter the interior of the frac-ball 50 upon failure of the structurally weakened regions 68. As a result, all interior surfaces of the frac-ball 50 are exposed to well casing fluid (as well as the exterior surfaces) and are subject to erosion, corrosion, or dissolution. The amount of time required for the entire frac-ball 50 to assume an inconsequential form (e.g., complete structural failure) is therefore greatly reduced. At the same time, however, the frac-ball 50 permits fluid flow through the frac-ball 50 and therefore fluid flow within the well casing.

Another significant aspect of the present disclosure frac-balls 50 is that they decrease the amount of time until fluid flow within the well casing can be resumed relative to certain solid frac-ball embodiments. The present disclosure frac-balls 50 also provide a mechanism that gives increased certainty to the time at which fluid flow within the well casing can be resumed. This increased certainty increases the efficiency of fracing a well that has a plurality of zones.

In those embodiments of the present disclosure frac-balls 50 that utilize an energetic material 80 to fracture the frac-ball 50 into discrete pieces, the present disclosure represents improvements over prior art exploding solid frac-balls. For example, the structurally weakened regions 68 facilitate the present frac-ball 50 fracturing into smaller discrete pieces than would likely be possible otherwise, particularly if the frac-ball 50 has a hollow configuration. The smaller discrete pieces by themselves are desirable because they decrease the possibility of a discrete piece creating a fluid flow impediment within the well casing. In those frac-ball 50 embodiments made of a material that erodes, corrodes, or dissolves upon exposure to a well casing fluid, however, the smaller discrete pieces also greatly increase the amount of frac-ball 50 surface area exposed to the well casing fluid, which in turn decreases the amount of time required for those discrete pieces to erode, corrode, or dissolve into inconsequential size.

Another significant aspect of the present disclosure frac-balls 50 is that they can be tailored to have a predetermined mechanical strength when operating as a sealing plug disposed within the seat of a segmentation device, and at the same time be tailored to fail (e.g., via the structurally weakened regions 68) at a predetermined pressure. Hence, the present disclosure provides a user with a device capable of satisfying the sealing requirements, as well as a device that can be altered to permit fluid flow in a controlled manner. Tailoring both the sealing strength and the failure mode can be achieved in a variety of different ways as indicated above; e.g., varying the number, geometry, and location of the structurally weakened regions 68, coupled with the varying the frac-ball wall thickness, etc.

According to an aspect of the present disclosure, a method of controlling fluid flow through a well casing segmentation device is provided. The method includes disposing an impermeable frac-ball in a seat of a well casing segmentation device to close a fluid passage of the well casing segmentation device, wherein the frac-ball includes at least one structurally weakened region, and causing an elevated pressure event adequate to cause the at least one structurally weakened region to fail, thereby opening the fluid passage of the well casing segmentation device.

As described above, in some embodiments the frac-ball 50 may include an interior cavity 60 and an energetic material and a trigger mechanism disposed within the interior cavity 60, and the trigger mechanism may be configured to selectively initiate the energetic material. In these embodiments, the step of causing the elevated pressure event adequate to cause the at least one structurally weakened region to fail includes causing the trigger mechanism to initiate the energetic material.

While the invention has been described with reference to several exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed herein as the best mode contemplated for carrying out this invention. 

What is claimed is:
 1. A frac-ball for use with a well casing segmentation device, the frac-ball comprising: a body having a shell configuration defined by one or more walls, with each wall having an exterior surface and an interior surface; wherein the interior surfaces define an enclosed interior cavity; and one or more structurally weakened regions disposed in the one or more walls.
 2. The frac-ball of claim 1, wherein the one or more structurally weakened regions have at least one physical characteristic different from a portion of the wall surrounding the structurally weakened region.
 3. The frac-ball of claim 2, wherein the one or more structurally weakened regions each possess mechanical strength properties adequate to avoid failure within a range of predetermined well environment operating parameters and/or for a predetermined period of time in a well casing environment.
 4. The frac-ball of claim 1, wherein the one or more walls each have a thickness extending between the exterior surface and the interior surface, and at least one of the structurally weakened regions is a pocket disposed in the wall, which pocket results in a decreased wall thickness.
 5. The frac-ball of claim 4, wherein the pocket is disposed in the interior surface of the wall, or in the exterior surface of the wall.
 6. The frac-ball of claim 4, wherein a plurality of the structurally weakened regions are pockets, at least one of which pockets is disposed in the interior surface of the wall and at least one of which pockets is disposed in the exterior surface of the wall.
 7. The frac-ball of claim 1, further comprising an energetic material and a trigger mechanism, the trigger mechanism configured to selectively initiate the energetic material.
 8. The frac-ball of claim 7, wherein the energetic material and trigger mechanism are disposed within the interior cavity of the frac-ball.
 9. The frac-ball of claim 8, wherein the energetic material and trigger mechanism are configured to produce an elevated pressure event adequate to cause the structurally weakened regions to fail.
 10. The frac-ball of claim 9, wherein the energetic material and trigger mechanism are configured to produce an elevated pressure event within the interior cavity adequate to cause the structurally weakened regions to fail in a manner that causes the frac-ball to rupture into discrete pieces.
 11. The frac-ball of claim 9, wherein the energetic material and trigger mechanism are configured to produce an elevated pressure event within the interior cavity adequate to cause the structurally weakened regions to fail in a manner that produces fluid passages through the frac-ball.
 12. The frac-ball of claim 9, wherein the one or more structurally weakened regions disposed in the one or more walls each include a plug disposed within an aperture disposed within the one or more walls; and wherein the energetic material and trigger mechanism are configured to produce an elevated pressure event within the interior cavity adequate to cause each plug to dislodge from the one or more walls.
 13. The frac-ball of claim 1, wherein the frac-ball body is comprised of a first material that erodes, corrodes, or dissolves at a first rate when contacted with a well casing fluid, and a plug comprised of a second material that erodes, corrodes, or dissolves at a second rate when contacted with a well casing fluid is disposed in each structurally weakened region, and the second rate is greater than the first rate.
 14. A method of controlling fluid flow through a well casing segmentation device, comprising: disposing an impermeable frac-ball in a seat of a well casing segmentation device to close a fluid passage of the well casing segmentation device, wherein the frac-ball includes at least one structurally weakened region; and causing an elevated pressure event adequate to cause the at least one structurally weakened region to fail, thereby opening the fluid passage of the well casing segmentation device.
 15. The method of claim 14, wherein the frac-ball includes an interior cavity and an energetic material and a trigger mechanism disposed within the interior cavity, the trigger mechanism configured to selectively initiate the energetic material; and wherein the step of causing the elevated pressure event adequate to cause the at least one structurally weakened region to fail includes the trigger mechanism initiating the energetic material.
 16. The method of claim 15, wherein the at least one structurally weakened region is configured to fail in a manner that causes the frac-ball to rupture into discrete pieces upon initiation of the energetic material.
 17. The method of claim 15, wherein the at least one structurally weakened region is configured to fail in a manner that produces one or more fluid passages through the frac-ball upon initiation of the energetic material.
 18. The method of claim 15, wherein the frac-ball includes at least one wall having a thickness extending between an exterior surface and an interior surface, and the at least one structurally weakened region is a pocket disposed in the wall, which pocket results in a decreased wall thickness.
 19. The method of claim 18, wherein the at least one structurally weakened region has at least one physical characteristic different from a portion of the wall surrounding the structurally weakened region.
 20. The method of claim 19, wherein the at least one structurally weakened region possesses mechanical strength properties adequate to avoid failure within a range of predetermined well environment operating parameters and/or for a predetermined period of time in a well casing environment. 